Mechanisms of synaptic transmission in the vertebrate retina and its role in visual information processing will be stdied by intracellular recording from single identified neurons in the retina of the mudpuppy, Necturus maculosus. Different suspected neurotransmitter substances, specific antagonists to these substances and agents which block transmitter release from presynaptic terminals will be applied to the retina by a superfusion technique. The nature of the synaptic inputs to different cell types will characterized and candidates for the transmitter substance mediating the different inputs will be evaluated. The effect of specific antagonists on the responses to both applied and endogeous transmitter substances will be studied. The ionic basis of the different types of postsynaptic responses will be studied by ionic substituton of the perfusing medium. Individual neurons recorded from will be morphologically identified by injecting the flourescent dye Lucifer yellow into the neuron at the time of recording.